Vibratory conveyor system

ABSTRACT

A vibratory conveyor system for use in the treatment of material as it is being conveyed (e.g., freeze dried), such system being in the form of a frame composed of conduit means for heat exchange medium and superposed vibratory conveying decks having conduit means for the heat exchange fluid below the surface thereof. In a specific system, four superposed conveying decks are mounted on springs and driven from a common drive shaft via eccentrics and rockers so that the vertical and horizontal forces cancel each other, the decks having coils to conduct cooling (or heating) fluid and the longitudinal members of the supporting frame being tubular to receive the same fluid so that they will change lengths as the decks change length in response to temperature changes.

United States Patent which is a continuation of Ser. No. 772,944, Nov. 24, 1968, abandoned.

U.S. Cl ..34/92, 62/266, 34/ 164, Q

Int. Cl. ..F26b 13/10 Field of Search ..34/164, 5, 92, 76, 84, 172,

Rowell 1 June 6, 1972 541 VIBRATORY CONVEYOR SYSTEM [56] CM [72] Inventor: Lorne A. Rowell, Lachine, Quebec, FOREIGN PATENTS 0R APPLICATIONS Canada 757,728 9/1953 Great Britain ..34/5 73 Assi nee: oh T.H rt l-l' dal ,lll. J g J n 0 ms e Primary Examiner.lohn J. Camby [22] Filed: Dec. 24, 1970 Assistant Examiner-W. C. Anderson Att Flh,H hb h,T t,Alb'tt &H brt [21] APPLNO': 101,343 orney e r 0 ac es n on er e [57] ABSTRACT Related us'AppucationDam A vibratory conveyor system for use in the treatment of [63] continuationdmpan of 9J02, Feb. 9, 1970, material as it is being conveyed (e.g., freeze dried), such system being in the form of a frame composed of conduit means for heat exchange medium and superposed vibratory conveying decks having conduit means for the heat exchange fluid below the surface thereof. In a specific system, four superposed conveying decks are mounted on springs and driven from a common drive shaft via eccentrics and rockers so that the vertical and horizontal forces cancel each other, the decks having coils to conduct cooling (or heating) fluid and the longitudinal members of the supporting frame being tubular to receive the same fluid so that they will change lengths as the decks change length in response to temperature changes.

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VIBRATORY CONVEYOR SYSTEM CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending application Ser. No. 9,102, filed Feb. 9, 1970, which is a continuation of my previously filed application, Ser. No. 772,944, filed Nov. 24, 1968, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates generally to vibratory conveyor systems for conveying materials and exposing them to a controlled environment, and more particularly to vibratory onveyor systems useful in the freeze drying of liquid foods such as coffee, tea, fruit juices and the like, and wherein processing is carried out continuously in a relatively short period of time.

If a straightforward single vibratory conveyor were used for conveying the material, it would have to be extremely long and, of course, the chamber in which the process is carried out would have to be correspondingly long. Moreover, the floor vibrations and mechanical fatigue of the driving components of the conveyor would present serious problems. Also when used in processing involving temperature extremes, such as freeze drying, differential expansion and contraction of the vibratory conveyor components, support members, fluid lines and the like would present serious problems in the use and operation of the equipment.

SUMMARY OF THE INVENTION AND OBJECTS In accordance with the invention, a vibratory conveyor system is provided in the form of a support frame and a multilevel vibratory pathway, the frame and each level of the vibratory pathway having interconnecting conduit'means for heat exchange medium so that the frame and vibratory pathway may be maintained at substantially the same temperature while the vibratory pathway is being vibrated at an optimum frequency. Such construction permits a minimum of interference with the processing conditions or the functioning of the apparatus due to vibration or changes in dimension due to temperature.

In a disclosed embodiment of the vibratory conveyor system, the frame is composed of horizontally extending members and upright members between said horizontally extending members which are formed as fluid conduit means adapted to conduct heat transfer fluid therethrough to vertically spaced components of the conveyor means. The conveyor means, in turn, is in the form of a series of vertically spaced conveying decks mounted within the frame, each having passage means for conducting heat transfer fluid therethrough to produce a desired temperature on the surface of the conveying decks. Since the heat transfer fluid passes simultaneously through the fluid conduit means of the frame and the passage means of the conveying decks, the frame will change length as the decks change length in response to temperature change, thereby minimizing the effects of changes in dimension due to temperature. Vibrator means, which may be carried by the frame, operate to vibrate pairs of the conveying decks in opposed vertical and horizontal relation with respect to one another, to thereby minimize the transfer of vibratory forces to the frame. In a preferred system of apparatus, four vertically spaced conveying decks are mounted in superposed relationship on the upright members of the frame by means of flat springs which extend at an angle to the upright members. The vibratory means makes use of a first rocker means connected by flat springs to two of the decks and a second rocker means connected to the other two of the decks, said rocker means being operated by diametrically opposed eccentric means so as to effect a cancelling of vertical and horizontal vibratory forces transmitted by the eccentrics to the rockers. The net effect is a minimum interference with the processing conditions or the functioning of the apparatus as a result of vibration, and a minimum transference of vibratory forces to stationary components of the support structure.

It is an object of the present invention, therefore, to provide a vibratory conveyor system which is relatively compact, which is relatively unaffected by changes in dimension due to temperature, and which minimizes floor vibration, mechanical fatigue, and other detrimental effects of continued prolonged vibration.

Another object of the invention is to provide a vibratory conveyor system of such character which is constructed to minimize the eflects of differential change in length of support and conveying surfaces due to temperature change.

A further object of the invention is to provide a novel vibratory conveyor system of such character adapted to use within an evacuated freeze drying chamber.

Further objects and features of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 and 2 are a view in vertical elevation of a freeze drying chamber useful in conjunction with the method and the system of apparatus of the present invention.

FIG. 3 is a view in transverse section along the line 33 of FIG. 2.

FIG. 4 is a like view along the line 44 of FIG. 1.

FIG. 5 is an enlarged view of a portion of the apparatus of FIG. 3, takenalong the line 5-5 thereof.

FIG. 6 is an enlarged view of a portion of the apparatus of FIG. 2, taken along the line 66 of FIG. 5.

FIG. 7 is a further enlarged detail view taken along the line 7-7 of FIG. 6.

FIG. 8 is a like view taken along the line 88 of FIG. 6.

FIG. 9 is a like view in top plan taken along the line 9-9 of FIG. 6.

FIG. 10 is a like view in bottom plan taken along the line 10l0 ofFIG. 6.

FIG. 11 is a sectional view taken along the line 1l-ll of I FIG. 9.

FIG. 12 is a further enlarged detail view along the line l2- 12 of FIG. 6.

FIG. 13 is a like view along the line 13-l3 of FIG. 12.

FIG. 14 is a like view along the line 14-14 of FIG. 6.

FIG. 15 is a like view along the line l5l5 ofFIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENT For illustrative purposes, the apparatus will hereinafter be described in conjunction with a system for freeze drying frozen particles of a liquid extract, for example, discrete particles of frozen coffee extract. It will be understood, however, that the described apparatus can be satisfactorily employed in a wide variety of processes involving simultaneous heat exchange and vibratory conveyance.

As illustrated in FIG. 1, the freeze drying is carried out in an evacuated substantially air-free chamber 42. To maintain desired conditions within the chamber, frozen particles are fed at appropriate intervals through a vapor lock (not shown) to an internal feed hopper 50 within the drying chamber 42, from which the frozen particles are fed to a controllable vibrating feeder 52 at a regulated, uniform rate to vibratory conveyer means within the freeze drying chamber. As illustrated, the vibratory conveyer means comprises a series of vertically spaced vibrated conveying decks, 54, 56, 58 and 60, hereinafter more fully described. In the described embodiment, the individual conveying decks are cooled to maintain desired characteristics of the particles as they are freeze dried, while the particles are simultaneously subjected to radiant energy to sublimate the ice content to vapor form. As also hereinafter described, the vibratory conveyer means is bounded on each side by a series of condensers 62 (See FIG. 3), which are maintained at a suitably low temperature (i.e., 50 to l00 F.) by suitable refrigerating media such as liquid cryogens. In general, the condensers function as highspeed pumps and maintain a low pressure by causing water vapor and other condensible gases to condense and freeze on the cold surfaces of the condenser plate.

As viewed in FIG. 1, frozen particles fed to the top conveying deck move with a bouncing or dancing motion to the right of the chamber, and are periodically rotated and turned over by the vibrating action of the conveyer. Upon reaching the end of the conveyer 54, the particles fall and are deflected onto the sub-adjacent conveying deck 56 where the conveying action is repeated until, upon reaching the endof the conveying deck 56, the particles again fall and are deflected onto the deck 58 below. The particles continue along the vibrating pathway provided by the deck 58 until they fall again to the sub-adjacent conveyer 60, where the vibrating conveyance is repeated until the particles eventually fall intov the product hopper 74. Throughout the-progression along the vibrating pathway of the conveyers 54, 56, 58 and 60, the ice content of the frozen particles is efiectively sublimated and removed by transfer to the condenser plates 62. The latter are periodically de-iced by surges of warm refrigerating means with the result that the ice falls to the bottom of the chamber where it is collected on a belt conveyer 76 for removal from the system, for example, through a suitable vapor lock containing breaker means 86.

The vibratory conveyor system of the present invention provides a particular advantage through its ability to avoid interference with controlled conditions of equilibrium within the freeze drying chamber, through transmittal of heat or vibratory forces to the chamber, and, also, because the conveying decks themselves are not materially afiected by changes in temperature within the freeze drying chamber.

As best illustrated in FIGS. 1 through 4, the vibrating conveyor means (generally represented at 180) comprise pairs of vertically spaced conveying decks 54, 56 and 58, 60, mounted in superimposed relationship within a supporting, fluid conducting tubular framework 182 which, in turn, is suspended from the top of the freezedrying chamber42. The suspension mounting, including freely supported pivot members 184, serves to isolate. the vibratory conveyor and its vibrating mechanism from the freeze drying chamber, thereby minimizingtransfer of vibratory forces to the chamber. The separate conveying decks are likewise resiliently mounted within the tubular frame 182 by means of flat springs 186, 188, 190 and 192, at spaced intervals along the full length of the conveying decks, as hereinafter described.

As particularly illustrated in FIGS. 3 to 5, the tubular frame 182 comprises upper longitudinally extending members 194 and 196 and lower longitudinally extending members 198 and 200, which are of hollow tubular construction to facilitate the circulation therethrough of the cooling liquid. The frame also comprises transverse bracing members 202 and vertical bracing members 204 which, if desired, may also be of hollow tubular construction to interconnect with the members 194, 196, 198 and 200 laterally and vertically. As noted previously, the tubular frame can be supplied with cooling liquid to equalize the same with temperature change.

The separate conveying decks, 54, 56, 58 and 60 are similar in construction and, since a balanced system is desired, are generally of equal size and weight and of substantially the same length. As best illustrated in FIGS. 9 and 10, the upper surface of each deck is formed of a series of overlapping plate sections 210 which are connected to the side frames of the decks adjacent one lateral edge 207, as at 209, so as to permit a sliding length adjustment adjacent the other lateral edge 211,-which rests in free sliding relation above the connected edge portion of the adjacent plate section 210. As illustrated, each individual plate section is provided with a cooling coil 212 beneath the upper place surface, which is supplied with cooling fluid from the line 154 by means of flexible conduit (not shown) interconnecting the integral fluid supply conduits 213 of each of the decks (see FIG. 13). The decks with their overlapping plate surfaces are individually vibrated in the manner hereinafter described so that the frozen particles move along the series of plates 210 which form the conveying surface. Because of the overlap between the plates 210, the output ends will be slightly higher than the input ends so that the material being conveyed will be turned over as it passes from one plate surface to the next, thereby insuring a more uniform freeze drying of the material.

As previously noted, the separate conveying decks are resiliently mounted for vibration within the frame 182 by means of pairs of flat springs clamped at one end to the decks and at the other end to the vertical bracing members 204 of the frame. Thus, as is particularly illustrated in FIGS. 6 through 8, the top conveying deck 54 is supported in an upwardly spaced relationship by pairs of flat springs 186, secured to'the deck by clamp means 218 and to the uprights 204 by clamp means 220 (FIG. 7). The conveying deck 56 next below is similarly supported in downward depending fashion by pairs of flat springs 188, secured to the deck by the clamp means 222 and to the uprights by the clamp means 224. In general, the angles of inclination and declination of the pairs springs 186 and 188 are substantially identical, and are chosen to achieve optimum characteristics of movement of the frozen particles along the conveyer decks. As best illustrated in FIGS. 2 and 6, the lower decks 58 and 60 are mounted for vibration within the frame 182 in substantially identical fashion to the upper pair of decks, by the pairs flat springs 190 and 192.

Referring to FIG. 6, it will be noted that the upper conveying decks 54 and 56 are mounted for vibration as a pair in conjunction with a rocker arm 230 whereas the lowerconveying decks 58 and 60 are likewise mounted as a pair for vibration by the rocker arm 233. The drive means for vibrating the pairs of decks 54, 56 and 58, 60 comprises a motor 234 which is preferably mounted exteriorly of the freeze drying chamber. The motor operates through a flexible shaft 236 to drive pairs of eccentrics 238 and 240 associated with the rocker arms 230 and 233, respectively. As will be apparent from FIGS. 5 and 6, the two eccentrics 238 and the two eccentrics 240 are out of phase with one another so as to be diammetrically opposed. That is, as the two eccentrics 238 move to rotate the extending arms 242 of the rocker arm 230 in a clockwise direction (as viewed in FIG. 6), the two eccentrics 240 move to rotate the arms 244 of the rocker arm 233 in a counterclockwise direction. As, the rotation of the eccentrics continues, the direction of rocker arms 242 and 244 will reverse. It will be seen that the horizontal direction of movement of the upper and lower decks 54 and 60 will always be the same, and the horizontal movement of the intermediate decks 56 and 58 will also be the same, but in a direction opposite to that of decks 54 and 60, thus balancing the horizontal forces within the framework. In contrast, when upper deck 54 moves up, the lower deck 60 moves down and, in like fashion, the upper middle deck 56 will move up when the lower middle deck 58 moves down, thus balancing the vertical forces within the framework. The described operation thus provides a balanced vibratory motion between the pairs of decks, which holds true for any position of the vibrating cycle.

In the mounting of the eccentric drive members, it will be understood that the rocker members 230 and 233 are mounted for free rotation, respectively, on transverse shafts 246 and 248 carried by the frame. The eccentrics 238 are connected to the rocker arms 230 by flat springs 250 and the rocker arms 242 are similarly connected to the conveying decks 54 and 56 by flat springs 252, such construction providing desired resiliency. In like fashion, the eccentrics 240 are connected to the rocker arms 233 by flat springs 254 and the rocker arms 244 are connected to the conveying decks 58 and 60 by the flat springs 256. Power requirements are greatly reduced in the described balanced system because the stored energy at the end of each stroke is returned to the decks in opposing directions, less a small loss due to friction. Consequently, once the system has reached its natural operating frequency, the only additional energy to be supplied by the drive through the eccentrics is the small amount required to replenish the friction losses.

It will be apparent from the foregoing that the fundamental (static and dynamic) forces of vibration generated by the four conveying decks tend to cancel one another out within the frame 182 so that transference of vibratory forces from the frame to the freeze drying chamber 42 is minimized.

In general, the amplitude of vibration as well as the "pitch" and throw of the conveyer decks 54 60 is dependent upon the construction and arrangement of the eccentrics 238 and 240, the rocker arms 230 and 233, and the flat springs 186, 188 and 190, 192. In like fashion, the frequency of the vibration is dependent upon the rotary speed of the motor 234 and the rotary speed (i.e., rpm) of the drive shaft 236. To insure that the forces handled by the drive components are kept at a minimum, resulting in smaller and lighter drive members, it is desirable to drive the spring mounted system at its natural frequency. This is accomplished in the described system of apparatus by the use of drive connections (e.g., components 250 to 256) and conveyer deck supports (e.g., components 186 to 192) which are in the form of flat springs selected to have the necessary rigidity to produce a natural frequency of vibration of the system approximating the frequency of the eccentric drive as hereinbefore defined. As a practical matter, of course, appropriate spring members may be selected and the drive cycled to achieve a condition which matches the natural frequency vibration of the spring mounted system.

ln a general operation of the vibratory conveyer means described, frozen particles are advanced first along the upper conveyer deck 54 where they are subjected to cooling from below and to radiant heating by a source of radiant energy (not shown) located above the upper deck. Partially freeze dried particles discharged over the end of the conveyer deck 54, at 68, pass in sequence to the vibratory conveying decks 56, 58 and 60 below. In each pass on these decks, they are cooled from below by the internal cooling means 212 while simultaneously being heated from above by the source of radiant energy 214 carried by the conveying deck next above. Freeze dried particles ultimately pass to the hopper 74 for discharge from the system, in the manner previously described.

Many variations are possible in the herein described arrangement and use of the disclosed system of apparatus. For example, although the disclosures relate to use of the apparatus in the freeze drying of solids-containing aqueous liquids, the apparatus could be easily adopted to many other uses and applications, for example, drying solid or semi-solid particulate materials, freezing particulate materials, heat treating (viz., toasting), dehydration of various unfrozen materials and, in fact, virtually any process or treatment wherein combined temperature control and vibratory conveyance would be useful or of advantage. In processes to heat treat (or toast) the product, it will be understood that a heat exchange fluid of higher temperature than the product would be introduced to the tubular frame and to the coils of the conveyance decks, to equalize the same with temperature change. Use of an enclosure or evacuated chamber 42 could also be dispensed with, in a system of apparatus operated at atmospheric condition. Many other and additional variations will similarly occur to those skilled in the art, and can be easily adapted to the disclosed system of apparatus without appreciable change in the structure or concept. Accordingly, it should be understood that the disclosures herein are purely illustrative and not in any sense limiting.

I claim:

1. A vibratory conveyor system comprising a frame having horizontally extending members and upright members between said horizontally extending members, vibratory conveyor means comprising vertically spaced conveying decks mounted within said frame, said vibratory conveyor means including means to vibrate said vertically spaced conveying decks, fluid passage means beneath the upper surface of each of said conveying decks for conducting fluid therethrough to produce a desired temperature on said decks, and passage means in said frame members for conducting fluid therethrough of a temperature similar to that of the fluid passing through the deck passage means whereby effects of change of length of said decks caused by change in temperature are minimized.

2. In apparatus for the treatment of material in particulate form as it is being conveyed, a frame having horizontally extending members and upright member between said horizontally extending members, conveyor means in the form of a series of vertically spaced conveying decks mounted within said frame, passage means for conducting a heat transfer fluid through each of said conveying decks to produce a desired temperature on said decks, said frame being formed of fluid conduit means adapted to conduct heat transfer fluid therethrough to the passage means in each of said vertically spaced conveying decks whereby the frame will change length as the decks change length in response to temperature changes, and vibrator means adapted to vibrate pairs of said conveying decks in opposed vertical and horizontal relation with respect to one another to minimize the transfer of vibratory forces to said frame.

3. Apparatus as in claim 2 wherein said conveying decks are mounted as a spring supported system within the frame by means of flat springs which extend at an angle to said upright frame members. 1

4. Apparatus as in claim 3 wherein said vibrator means is operated to achieve a frequency of vibration of said spring supported system approximately equal to the natural frequency of said system.

5. A vibratory conveyor system comprising a frame having horizontally extending members and upright members between said horizontally extending members, first, second, third and fourth vertically spaced conveying decks mounted in superposed relationship on said upright members by means of flat springswhich extend at an angle to said upright members, first rocker means at one end of the frame and connected by flat springs to said first and second decks, second rocker means at said one end of the frame and connected by flat springs to said third and fourth decks, driving means, a shaft driven by said driving means, first and second diametrically opposed eccentric means on said shaft, flat springs connecting said first and second eccentric means with said first and second rocker means, respectively, passage means beneath the upper surface of each of said decks for conducting fluid therethrough to produce a desired temperature on said decks, and passage means in said horizontally extending frame members for conducting fluid therethrough of a temperature similar to that of the fluid passing through the deck passage means whereby to minimize the effects of change of length of said decks caused by change in temperature thereof.

6. A vibratory conveyor system as claimed in claim 5, wherein each of said decks comprises a plurality of trays, each of which has one end higher than the adjacent end of a succeeding tray so that material being conveyed along a said deck will be turned over as it leaves the higher end of a preceding tray and is deposited on the end of the next tray.

7. A system of apparatus for continuously freeze drying particles of frozen material comprising: a closed freeze drying chamber, vibratory conveying means for moving said particles of frozen material through said freeze drying chamber, said vibratory conveying means including pairs of vertically spaced conveying decks mounted in superimposed relationship within a tubular fluid conducting frame, said tubular frame being suspended within said freeze drying chamber, vibrating means including diametrically opposed eccentric means to oppositely vibrate said pairs of spaced conveying decks, drive means for said opposed eccentric means mounted exteriorly of said freeze drying chamber, said spaced conveying decks being supported within said tubular frame by flat springs providing a natural frequency of vibration equal to the frequency imparted to said spaced conveying decks by said vibrating means, passage means beneath the upper surface of each of said vertically spaced conveying decks for conducting heat exchange fluid therethrough to produce a desired temperature on said decks, and passage means in said tubular frame for conducting heat exchange fluid therethrough to the passage means of said conveying decks, whereby the effect of vibration and difi'erential change in length of said decks and tubular frame caused by change in temperature are minimized. 

1. A vibratory conveyor system comprising a frame having horizontally extending members and upright members between said horizontally extending members, vibratory conveyor means comprising vertically spaced conveying decks mounted within said frame, said vibratory conveyor means including means to vibrate said vertically spaced conveying decks, fluid passage means beneath the upper surface of each of said conveying decks for conducting fluid therethrough to produce a desired temperature on said decks, and passage means in said frame members for conducting fluid therethrough of a temperature similar to that of the fluid passing through the deck passage means whereby effects of change of length of said decks caused by change in temperature are minimized.
 2. In apparatus for the treatment of material in particulate form as it is being conveyed, a frame having horizontally extending members and upright member between said horizontally extending members, conveyor means in the form of a series of vertically spaced conveying decks mounted within said frame, passage means for conducting a heat transfer fluid through each of said conveying decks to produce a desired temperature on said decks, said frame being formed of fluid conduit means adapted to conduct heat transfer fluid therethrough to the passage means in each of said vertically spaced conveying decks whereby the frame will change length as the decks change length in response to temperature changes, and vibrator means adapted to vibrate pairs of said conveying decks in opposed vertical and horizontal relation with respect to one another to minimize the transfer of vibratory forces to said frame.
 3. Apparatus as in claim 2 wherein said conveying decks are mounted as a spring supported system within the frame by means of flat springs which extend at an angle to said upright frame members.
 4. Apparatus as in claim 3 wherein said vibrator means is operated to achieve a frequency of vibration of said spring supported system approximately equal to the natural frequency of said system.
 5. A vibratory conveyor system comprising a frame having horizontally extending members and upright members between said horizontally extending members, first, second, third and fourth vertically spaced conveying decks mounted in superposed relationship on said upright members by means of flat springs which extend at an angle to said upright members, first rocker means at one end of the frame and connected by flat springs to said first and second decks, second rocker means at said one end of the frame and connected by flat springs to said third and fOurth decks, driving means, a shaft driven by said driving means, first and second diametrically opposed eccentric means on said shaft, flat springs connecting said first and second eccentric means with said first and second rocker means, respectively, passage means beneath the upper surface of each of said decks for conducting fluid therethrough to produce a desired temperature on said decks, and passage means in said horizontally extending frame members for conducting fluid therethrough of a temperature similar to that of the fluid passing through the deck passage means whereby to minimize the effects of change of length of said decks caused by change in temperature thereof.
 6. A vibratory conveyor system as claimed in claim 5, wherein each of said decks comprises a plurality of trays, each of which has one end higher than the adjacent end of a succeeding tray so that material being conveyed along a said deck will be turned over as it leaves the higher end of a preceding tray and is deposited on the end of the next tray.
 7. A system of apparatus for continuously freeze drying particles of frozen material comprising: a closed freeze drying chamber, vibratory conveying means for moving said particles of frozen material through said freeze drying chamber, said vibratory conveying means including pairs of vertically spaced conveying decks mounted in superimposed relationship within a tubular fluid conducting frame, said tubular frame being suspended within said freeze drying chamber, vibrating means including diametrically opposed eccentric means to oppositely vibrate said pairs of spaced conveying decks, drive means for said opposed eccentric means mounted exteriorly of said freeze drying chamber, said spaced conveying decks being supported within said tubular frame by flat springs providing a natural frequency of vibration equal to the frequency imparted to said spaced conveying decks by said vibrating means, passage means beneath the upper surface of each of said vertically spaced conveying decks for conducting heat exchange fluid therethrough to produce a desired temperature on said decks, and passage means in said tubular frame for conducting heat exchange fluid therethrough to the passage means of said conveying decks, whereby the effect of vibration and differential change in length of said decks and tubular frame caused by change in temperature are minimized. 